1. Technical Field
The disclosure relates generally to Lange couplers, and more particularly, to an on-chip millimeter wave Lange coupler.
2. Background Art
A 3 dB coupler having a 90° phase difference between the outputs of the 3 dB coupler is a very useful device in microwave and millimeter wave circuit design applications, such as high-frequency in-phase/quadrature (IQ) modulation and balanced amplifier structures. Such a 3 dB coupler can be realized, for example, as a branchline coupler or as a conventional Lange coupler. Normally, branchline couplers have a larger size and less frequency bandwidth than conventional Lange couplers, but the DC signals are shorted among all ports or DC paths exist among all ports.
For on-chip implementations, branchline couplers exhibit a better amplitude balance than conventional Lange couplers but they are much larger in size and, therefore, much more costly. Conventional on-chip Lange couplers utilize higher level metal layers for the signal traces so as to take advantage of the lower resistance loss, but the relatively larger minimum width and spacing of the design rule for those metal layers causes insufficient coupling among the lines and bad amplitude unbalance.